Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically or cytologically confirmed non-small cell lung cancer (NSCLC)

- Must have evidence of brain metastases by MRI or CT scan

- No single brain metastases or oligometastatic disease amenable to surgical
resection or radiosurgery

- Relapsed NSCLC with brain metastases allowed

- Not a candidate for double-agent or platinum-based chemotherapy

- No leptomeningeal metastases

- No clinically relevant (defined by physical exam) pleural effusions or ascites that
cannot be controlled with drainage or other procedures

PATIENT CHARACTERISTICS:

- Karnofsky performance status 70-100% OR ≥ 70 years of age

- Life expectancy > 3 months

- ANC > 1,500/mm³

- Platelet count > 100,000/mm³

- Hemoglobin ≥ 8 g/dL

- AST and ALT < 3 times upper limit of normal (ULN)

- Bilirubin ≤ 1.5 times ULN

- Creatinine clearance ≥ 45 mL/min

- No contraindication or intolerance to corticosteroid therapy

- No other malignancies within the past 5 years and disease-free OR prognosis is best
defined by the NSCLC in the opinion of the attending physician

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

- No HIV positivity

- No severe hypersensitivity to pemetrexed disodium

- Able to discontinue NSAIDs for ≥ 5 days

- No history of underlying dementia, Parkinson's disease, or Alzheimer's disease

- Able to take vitamins, folic acid, and corticosteroids

PRIOR CONCURRENT THERAPY:

- Recovered from prior oncologic or major surgery

- Prior resection of all brain metastases or only site of brain metastases allowed
provided there is radiologically evaluable intracranial metastases

- No prior cranial irradiation, including stereotactic radiosurgery

- More than 30 days since prior nonapproved or investigational drug

- No other concurrent chemotherapy, immunotherapy, hormonal therapy, radiotherapy,
surgery, or experimental medications